SWODY2
SPC AC 270517
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1217 AM CDT SUN SEP 27 2009
VALID 281200Z - 291200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODELS SUGGEST THAT A STRONGER MORE ZONAL UPPER FLOW ACROSS THE
NORTHERN TIER STATES...ASSOCIATED WITH A VIGOROUS JET STREAK
MIGRATING INLAND OFF THE NORTHERN PACIFIC...WILL TRANSITION TO A
MORE AMPLIFIED AND LESS PROGRESSIVE REGIME DURING THIS FORECAST
PERIOD. BY 12Z MONDAY...A STRONG DIGGING SHORT WAVE TROUGH ON THE
NOSE OF THE JET IS PROGGED TO CONTRIBUTE TO THE EVOLUTION OF A DEEP
LOW/MID TROPOSPHERIC CYCLONE OVER THE GREAT LAKES REGION. A SLOW
EASTWARD PROGRESSION TOWARD THE ST. LAWRENCE VALLEY MAY CONTINUE
THROUGH 12Z TUESDAY...AS ANOTHER AMPLIFIED TROUGH DIGS SOUTHEASTWARD
OUT OF THE NORTHEAST PACIFIC. IT APPEARS THAT ONE SIGNIFICANT
IMPULSE EMBEDDED WITHIN THIS LATTER FEATURE WILL DIG SOUTHWARD
THROUGH CENTRAL PACIFIC COASTAL AREAS...WHILE ANOTHER TURNS INLAND
ACROSS THE BRITISH COLUMBIA COAST INTO THE CANADIAN ROCKIES.
IN THE WAKE OF AN INCREASINGLY SHEARED UPPER TROUGH PROGRESSING EAST
OF MUCH OF THE ATLANTIC SEABOARD IN ADVANCE OF THE DEVELOPING
CYCLONE...HIGH MOISTURE CONTENT AIR APPEARS LIKELY TO BE ADVECTED
SOUTH AND EAST OF ALL BUT THE SOUTHERN FLORIDA PENINSULA AND
SOUTHERN TEXAS BY THE BEGINNING OF THIS FORECAST PERIOD. WHILE
DESTABILIZATION IN THESE AREAS WILL PROBABLY BECOME SUFFICIENT FOR
AT LEAST SCATTERED THUNDERSTORM ACTIVITY...CONVECTIVE POTENTIAL
ACROSS MUCH OF THE REMAINDER OF THE NATION APPEARS LOW.
...UPR OH VLY INTO THE LEE OF THE LWR GREAT LAKES...
MODEL FORECAST SOUNDINGS ARE SUGGESTIVE THAT LIMITED MOISTURE
COUPLED WITH RELATIVELY WARM AIR ALOFT WILL RESULT IN ONLY A
RELATIVELY SHALLOW LAYER OF WEAK INSTABILITY WITHIN THE WARM SECTOR
OF THE OCCLUDING CYCLONE. THUS...WHILE PRE-FRONTAL CONVECTIVE
ACTIVITY APPEARS PROBABLE IN RESPONSE TO STRONG DYNAMIC
FORCING...PARTICULARLY THROUGH MONDAY MORNING/AFTERNOON ACROSS PARTS
OF WESTERN NEW YORK/PENNSYLVANIA...UNCERTAINTY EXISTS AS TO WHETHER
THE CONVECTIVE LAYER WILL EXTEND DEEP ENOUGH INTO THE MIXED PHASE
LAYER FAVORABLE FOR CHARGE SEPARATION AND THE FORMATION OF
THUNDERSTORMS. EVEN IN THE ABSENCE OF STRONGER
CONVECTION...HOWEVER...DOWNWARD TRANSFER OF HIGHER MOMENTUM
ASSOCIATED WITH THE 40-50+ KT MEAN AMBIENT FLOW MAY BE ENOUGH FOR
SPORADIC POTENTIALLY DAMAGING WIND GUSTS.
..KERR.. 09/27/2009
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